Breccia is a clastic sedimentary rock that is composed of large (over two-millimeter diameter) angular fragments. The spaces between the large fragments can be filled with a matrix of smaller particles or a mineral cement which binds the rock together. The specimen shown above is about two inches (five centimeters) across.
What Are Sedimentary Rocks?
Sedimentary rocks are formed by the accumulation of sediments. There are three basic types of sedimentary rocks.
Clastic sedimentary rocks such as breccia, conglomerate, sandstone, siltstone, and shale are formed from mechanical weathering debris.
Chemical sedimentary rocks, such as rock salt, iron ore, chert, flint, some dolomites, and some limestones, form when dissolved materials precipitate from solution.
Organic sedimentary rocks such as chalk, coal, diatomite, some dolomites, and some limestones, form from the accumulation of plant or animal debris.
Photos and brief descriptions of some common sedimentary rock types are shown on this page.
Diatomite is a sedimentary rock with many uses. It is made up of the siliceous skeletal remains of diatoms, which are tiny single-celled algae. Diatomite is crushed into a powder known as "diatomaceous earth". It is lightweight, porous, relatively inert, and has a small particle size along with a large surface area. These properties make diatomaceous earth useful as a filtration media, a lightweight aggregate, a lightweight filler, an effective absorbent, and more.
Coquina is a type of limestone composed of calcium carbonate shells, shell fragments, and other sand-sized fossil debris. It forms in the shallow waters of coastal areas with a tropical or subtropical climate. The particles are weakly cemented together, and therefore coquina is a very porous material that can function as an aquifer or a reservoir for oil and natural gas. Public Domain photo by Mark A. Wilson of the Department of Geology, The College of Wooster.